Process for the preparation of 2-bromo 3-halo propene-1



United States Patent 3,271,466 PROCESS FOR THE PREPARATION OF Z-BROMO 3-HALO PROPENE-l 3,271,466 Patented Sept. 6, 1966 The yield of 2,3-dibromo propene-l is about from 60 to 80% calculated on the amount of bromine originally present; boiling point at 60 mm. Hg from 67 to 70 C.;

Hendricus Gerardus Peer, Hilversum, Netherlands, bromine 9 771%; ldennficanon t 2 2 assignor to The Nederlandse Organisatie voor Toege- 5 red analysis shows that the substance is indeed ipast-Natuurwetenschappelijk Onderzoek ten Behoeve mO propene-l. van Nijverlieid, Handel en Verlieer, The Hague, Nether- In this case no other substances and especially no tetralands, a corp ration of th N th rla s broino propane can be found in the reaction mixture nor No Drawing. Original applicatiol7hgiil'. (116, 119.1611, 82c; inthe fi l rod t 110W Patent 3,1 7 ate y The mixture of glacial acetic acid and 2,3-dibnomo prof pgg and this apphcatlon 1964 10 pene-l formed in the reaction can be separated by frac- Claims priority, application Great Britain, Mar. 28, 1960, 011211 dlsnnfmn- 10897/60 10S98/60; May 20 1960, 10,839/60 In other inert solvents tetrabromo propane 1 Claim. Cl. 260-654 (CH BrCBr CH Br) This application is a division of my copending United States patent application Serial No. 96,102, file-d March m y al be formed by the reaction between bromine 16 1961, now United States patent 3 197 514 and allene, although under specific conditions the process This invention relates to a process for the preparation leads to the formation of isllbstalltlally 2,3-dibmm0 of 2,3-dibromo propene-l and of 2-bromo 3-chloro pro- P P pene-l; in the specification and claims these products are Example 2 covered by the term Z-bromo 3-halo propene-l.

It has e n found that 3-ha10 P P can Allene is dissolved in 75 ml. of CHCl bromine disbe Obtained in a good Yield y reacting allene solved in 125 ml. of CHCI is added in the dark over a (CHZICZCH2) 2 period of 3 /2 hours while stirring, stirring is continued for an hour, the reaction mixture is shaken with an with either bromine or a mixture of bromine and chlorine aqueous Solution f NaHCO:, 5%) h i h Water In pfesenoe of an Inert Solvent: If 15 used and finally dried over anhydrous Na SO the chloroform 2,3-dlbr 01110 P P z j z 15 formedis removed by distillation and the residue is fractionated. If a mixture of bromine and chlorine is used 2-bromo The results are recorded in m L In the fi t 3'ChIOTO P P 2 2 U 13 formedond and fifth experiments the temperature is minus 17 C.;

The term inert solvent as used herein means a solvent i thg hi d experiment i i 20 C i h fourth i- Which, under the reaction conditions, does not PP Inent it is 30 C. This table shows that it is possible to ably react either with the reactants or with the reaction obtain dibromo propened as the main or even sole products; examples of such solvents are chloroform and 3 a io product, Th di-bromo compound i denoted by carbon tetrachloride. di-BP; the tetrabromo propane by tetra-BP.

TABLE I B can in ad d i Molar ratio, Fraction Yield percent Molar ratio,

ml. grains BT22 C3H4 diBP tetra-B P di-IBP tetra-BF di-BP tetra-BF 3, 357 12 0. 5 4 4-a 69 nil 100:0 2, 953 21. 3 i. 0 5 5-3 65 nil 100:0 3, 442 24. s 1. 0 e 6-a 61 4 07:3 2, 430 17. 4 1. 0 7 7-a 05 nil 100:0 3, 353 48. 3 2. 0 8 8a 20 26 50 The Z-bromo 3-halo propene-l as defined herein before Fraction No. 4 is 10.4 g. boiling at 68 to 72 C. at is a valuable compound for instance as a nematocide. 60 mm. Hg;

When working in a dilute system in glacial acetic acid, Fraction No. 4a is nil g.; the reaction of allene with bromine takes place at one of Fraction No. 5 is 17.1 g. boiling at 68 to 70 C. at the two double bonds of the allene only, the resulting mm. Hg; product being 2,3-clibromo propene-l. Fraction No. S-a is ni-l g.;

Exam 1 Fraction No. 6 is 18.9 g. boiling at 68 to 72 C. at

p 60 mm. Hg;

Into a solution of 44 cc. of bromine in 800 cc. of 60 Fraction No. 6a is 1.2 g. boiling at 123 to 140 C. at glacial acetic acid at room temperature, allene 17 mm. Hg;

Fraction No. 7 is 14.1 g. boiling at 67 to 69 C. at CH -CH 2 C 2) 60 mm. Hg;

is introduced at a rate of 20 cc. per minute until the F a ti N 7 i il;

solution becomes colourless. The introduction of allene F ti N 8 i 8 g. boiling at 68 to 72 C, at 60 is then stopped and nitrogen is passed through the reac- 1-I tion mixture in order to remove a possible excess of allene. F ti No, 8- i 145 g boiling at 123 to 133 C, at

The reaction mixture is then poured out into 1600 cc. 17 H 0f 1CeWflteT, Q ethfif 18 added While Cooling If instead of chloroform carbon tetrachloride is used with ice, the mixture is neutralised with aqueous NaOH under the same conditions as in Example 2, similar re- (20%). The ethereal layer is separated, dried over anhydrous sodium sulphate and fractionated.

sults are obtained; vide Table II. In all cases the temperature is 17 C.

TABLE II Bromine Fraction No. Yield, percent C3I'I4 m added in Molar ratio, Molar ratio,

moles moles 131 Cal-I4 di-BP :tctra-BP di-BP tetra-BF di-BP tctra-BP 0. 15 0. 075 0. 5 9 9-21 77 nil 100:0 0.15 0.15 1. 0 10-a 47 9 85: 0. 10 0.20 2. 0 11 11-8. 47. 6 17 74:26

In the first two experiments the yield is calculated on the total of bromine added; in the last experiment on C3H4.

Fraction No. 9 is 11.8 g. boiling at 68 to 69 C. at 60 mm. Hg;

Fraction No. 9a is nil g.;

Fraction N0. 10 is 14.5 g. boiling at 68C. at 60 mm. 7

Fraction No. 10-a is 5.0 g. boiling at 124 to 128 C. a 17 mm. Hg;

Fraction No. 11 is 10 g. boiling at 68 to 70 C. at 60 mm. Hg;

Fraction 11-a is 7.3 g. boiling at 126 to 140 C. at 17 mm. Hg;

2,3-dibromo propene-l can be used as a nematocide.

If instead of chloroform as the solvent methylene chloride is used, at 17 C. and 1 mol bromine per 1 mol of allene, a molar ratio of di-BP to tetra-BP of 93:7 is found.

As stated hereinbefore, 2-bromo 3-chloro propene-l is obtained if allene is reacted with a mixture of chlorine and bromine in the presence of an inert solvent.

The best results are obtained by using substantially equimolar quantities of chlorine and bromine.

Example 3 19.5 grams of bromine (0.12 mole) are introduced into a solution of 8.7 grams of chlorine (0.12 mole) in 243 grams of carbon tetrachloride. This solution is then slowly added dropwise in the dark and with a nitrogen atmosphere to a solution of 5470 ml. (0.245 mole) of allene in 350 grams of carbon tetrachloride at minus 30 C. The mixture is kept at this temperature for one hour and for a further two hours at +20 C. After this the reaction mixture 'is shaken with an aqueous solution of sodium bicarbonate (5%), then with water and is finally dried over anhydrous Na SO The solvent is removed by distillation and further distillation gives four fractions, vide Table III.

TAB LE III Weight Boiling point in 0. ne

in grams Fraction The third fraction consists substantially of 2-bromo 3- chloro propene-1 as is shown by chemical analysis, boiling point and infrared spectrography which produce values which are the same as those obtained with a control sample of 2-bromo-3-chloro propene-l.

Fraction 2 probably contains 2,3-dichloro propene. Fraction 4 probably contains tetrahalogenati-on products.

The yield of 2-bromo 3-chloro propene-l is 41% calculated on the allene consumed. It is possible to improve this yield by decreasing the amount of halogen used with respect tothe amount of allene.

The identification of the fractions is by infrared spectrography by determination of the halogen content and by refraction index. A typigal fraction consisting, of substantially solely 2,3-dibromo propene-l had a bromine content of 79.1 (theoretically it is and an A typical fraction consisting of substantially solely tetrabromo propane had a bromine content of 88.60 (theoretically it is 88.89) and an n =1.6158.

If Example 3 is repeated but instead of carbon tetrachloride as the solvent glacial acetic acid is used, there is a very substantial formation of 2-bromo 3-acetoxy pro pene-l and no 2-brom0 3-chloro propene-l can be found in determinable quantities. The possible reason of this behaviour will be explained below.

The reaction scheme is probably as follows. The chemical structure of allene is (1) CH =(2)C=(3)CH in which the figures between brackets denote the numbering of the carbon atoms.

In the presence of bromine a 'bromination takes place at one of the double bonds, say at the double bond between carbon atoms (2) and (3). This addition of bromine starts with a primary addition of a positive bromine Br -ion:

The structure (A) may be called a bromonium ion. This structure (A) seeks to be stabilized.

If the solvent is inert and bromine is the sole halogenation agent, said stabilization takes place by incorporation of a negative bromine Br-ion:

thus leading to the formation of 2,3-di'bromo propene-l.

If the solvent is inert and a mixture of bromine and chlorine is used it should be noted that such a mixture reacts as if it were the compound Br+Cl and consequently said stabilization takes place by incorporation of a negative chlorine Cl--ion:

(A) Cl- CH CBr- CH Cl thus leading to the formation of 2-bromo 3-ch1oro propene-l.

The examples show that a solvent such as glacial acetic acid is insert if halogenation is done with bromine. But if halogenation is done with a mixture of bromine and chlorine (i.e. with Br+Cl) it is not Z bromo 3-chloro propene-l which is formed but 2-bromo 3-acetoxy propene-l; this is accounted for by the fact that negative chlorine Cl--ions are markedly less nucleophil-ic then acetoxy-ions so that (A) is stabilized as follows:

thus leading to the formation of 2-bromo 3-acetoxy pro.- pene-l. In this case glacial acetic acid is not inert.

The fact that be solely using bromine and glacial acid as the solvent no 2-bromo 3-acetoxy propene-l is formed but 2,3-dibromo propene-l proves that the negative bromine Br--ion is more nucleophilic than the acetoxy-ion.

As appears from the examples and the tables the first step of the halogenation is an attack on only one of the two double bonds of allene and in some solvents and under certain conditions the addition of bromine stops at this stage. In other solvents such as ether there is a secondary addition at the second double bond of allene, leading to the formation of tetrabromo propane although even then this second addition can be suppressed to an appreciable extent by varying the ratio of bromine to allene.

Examples of the latter type of inert solvents are ether, benzene, dioxane ethyl acetate and carbon disulphide. In these solvents with an initial ratio of 1 mol bromine per 1 mol allene and bromination at 20 C. in the dark, in the final mixture about 3 to 4 mols. of 2,3-dibromo pro pene-l per 1 mol tetrabromo propane are found. By increasing the amount of allene to about 2 mol per mol of bromine the formation of the tetrabromo compound is suppressed in favour of the formation of the dibromo compound. In ether as the solvent and an amount of 2 moles of allene per mol of bromine, bromination in the dark at 0 C. leads to the formation of the dibromo compound in a molar ratio of about 9 moles per mol of the tetrabromo compound.

But with halogenated hydrocarbons such as carbon tetrachloride, chloroform and methylene chloride (CH CI the formation of the dibromo compound is very much more predominant than the formation of the tetrabromo compound even if an excess of bromine is used. In general better results are obtained at lower temperatures of reaction. For instance with methylene chloride as the solvent at +20 C. rather much tetrabromo propane is formed.

It is advisable to use a solvent having at a specified pressure a boiling point substantially different from the boiling point of the 2-bromo 3-ha1o propene-l for in such a case separation of said compound from the solvent can easily be done by fractional destillation.

Separation of the reaction product from a water-miscible inert solvent is also possible by adding to the reaction mixture a substance such as water which precipitates the reaction product. Other method for such a separation can easily be devised by any one, skilled in the art.

All experiments recorded in the examples and the tables are on a laboratory scale. The yields are calculated on the initial amount of bromine, unless otherwise stated. The yields do not add up to because some bromine gets lost, partly in unidentified products. It stands to reason that the yields may 'be substantially improved if the process is carried out in a large scale apparatus because then slight losses during the isolating steps have only a slight effect upon the yield.

What is claimed is:

A process for the production of 2-bromo-3-chloro-propene-l, which consists of the steps of reacting a mixture of substantially equimolar amounts of chlorine and bromine with a solution of allene in an inert liquid solvent selected from the group consisting of methylene chloride, chloroform and carbon tetrachloride and recovering said 2- bromo-3 -chloro-propene-1.

References Cited by the Examiner UNITED STATES PATENTS 2,973,393 2/1961 Monroe 260-654 3,009,967 11/1961 Monroe 260654 3,110,740 11/1963 Peer 260-654 3,197,514 7/1965 Peer 260654 OTHER REFERENCES Lespieau et al., Bull. Soc. Chem. (France), vol. 45, part 2, (1929) p. 632.

LEON ZITVER, Primary Examiner.

a K. V. ROCKEY, Assistant Examiner. 

